The invention relates to a keypad layout for alphabetic character input and, more particularly, to a keypad that has alphabetic characters arranged and distributed on the keys thereof in a highly regular and efficient manner.
The arrangement and distribution of alphabetic characters on alphanumeric keypads so that the keypad is easy to use and does not create excessive ambiguity in creating multiple words with the same key strokes is difficult to achieve due to the small size of the keypad. This problem is especially pronounced in those alphabets having greater numbers of characters than those of Roman based alphabets, e.g. twenty-six Roman letter alphabet. The alphabetic character layout is more easily done on keyboards for desktop systems adapted for two-handed input as the keyboard generally has thirty-six alphanumeric keys readily available for character placement. As is apparent, the fewer number of keys in keypads complicates layout designs, especially with those languages having large alphabets.
One goal in arriving at a keypad layout is that the characters appear on the keys in a regular or intuitive arrangement so that users can readily become familiar with where the different characters are located in the keypad. In this manner, the keypad is easier to use and allows the user to become more proficient in its use for fast and accurate input of the characters. The other goal is to distribute the characters efficiently so as to minimize the ambiguity created when a given sequence of key inputs is undertaken to form a word. Ambiguity is created when the same sequence can create multiple words. Each time the user has to go through the process of choosing a word among several, overall input speed and efficiency is slowed particularly where the number of words to be selected is high. Accordingly, it is desirable to distribute the characters such that a minimum of such multiple word formations can be created from a given sequence of key inputs.
One problem that is noted is that the most efficient distribution of characters on a keypad may not produce a very regular arrangement for ease of use of the keypad. On the flip side, the most regular arrangement of the characters on the keys will generally not be the most efficient distribution of the characters for low input ambiguity. For instance, the typical character layout on a keypad for the twenty-six Roman letter alphabet is having the characters appear in alphabetical order on a row-by-row basis. As is apparent, this is a highly regular layout that allows a user to quickly become familiar with the location of the letters in the keypad particularly with users having native languages that are read in a left to right fashion. On the other hand, the ambiguity of this layout is very high as commonly used letters appear on the same key and characters that are less commonly used also appear together, e.g. letters G, H, I on key 4 vs. letters W, X, Y on key 9. So, for example, the same sequence of key inputs that produces the word xe2x80x9cgoodxe2x80x9d will also produce six other words for a total of seven possible valid candidates from the same key stroke sequence.
Also, and as mentioned, this problem of finding the optimum balance between regularity and efficiency in the arrangement and distribution of alphabetic characters on a keypad is exacerbated where the number of characters in the alphabet is higher than that of the Roman alphabet. One such example is Chinese alphabets, and in particular the Chinese phonetic alphabet called xe2x80x9cBopomofo.xe2x80x9d Bopomofo is the first Mandarin Chinese phonetic alphabet officially endorsed by the Chinese government as a National Standard and has been enforced by the public school education system for several decades. It is still in widespread use today. Bopomofo has a set of 40 phonetic symbols which creates organizational problems in the small keypad setting, as described above.
One prior keypad layout for the Bopomofo alphabet is used on the NEC DB2100 mobile phone (FIG. 3). The NEC keypad layout essentially follows that of the typical keypad layout for the Roman alphabet in that the characters are arranged in order on a row-by-row basis. Each commonly known set of characters is on a single key except for key #3 which has two such sets. While this layout is highly regular, it does not consider input effectiveness and thus produces too much ambiguity. In this regard, almost all the twenty possible character combinations provided by the sequence of inputting key #1 followed by key #8 are valid. As is apparent, a given sequence of key inputs with the NEC Bopomofo keypad will not provide much information.
Another Bopomofo keypad layout is on Motorola""s CD928+ mobile phone (FIG. 2). This layout is significantly improved over the NEC keypad in terms of input efficiency as it attempts to distribute conflicting characters, such as those that are in the same character set, onto different keys. On the other hand, this distribution created a messy or irregular arrangement of the characters, and thus one that is difficult to master.
Accordingly, there is a need for a keypad layout having an improved combination of regularity and efficiency for textual input. More particularly, a keypad for Chinese text input, i.e. the Bopomofo phonetic alphabet, is needed having a highly regular and efficient layout.